Counter-rotating boat propeller drive

Abstract

A dual boat propeller structure is described for counter-rotation of the propellers. A housing is located outside the boat hull in alignment and connection with an engine shaft. The housing stores a conversion mechanism with which coaxially-mounted propeller shafts are brought into counter-rotation to correspondingly rotate the propellers. A strut interconnects the housing to the boat hull in a manner so as to reduce vibrations from the counter-rotating mechanism. The housing has a frusto-conical shape with which a large diameter aft end is sized commensurate with the hub of the propellers for smooth water flow.

What is claimed is: 
     
       1. A counter-rotating propeller system for boats having an inboard engine which rotates a drive shaft that extends in an aft direction through a lower part of the boat hull, comprising: first and second propellers, each of said propellers having a hub;   coaxially-mounted inner and outer propeller shafts, each shaft having a said propeller mounted at an aft end and with the inner propeller shaft being coupled in axial alignment to the drive shaft externally of the boat hull;   conversion means located externally to the boat hull and coupled in interlocked relationship to the inner propeller shaft for converting drive shaft rotation to counter rotation of the inner and outer propeller shafts;   a housing enclosing the conversion means, said housing having a forward open end through which said inner propeller shaft extends for coupling to the drive shaft and having an aft end from which the coaxial propeller shafts extend; and   a strut connected to the lower part of the boat hull and to the housing, the strut being sufficiently sized and shaped to rigidly support the housing while maintaining proper alignment of the conversion means with the drive shaft to reduce lateral vibrations, said strut further having a lateral crossectional area selected to present a streamlined shape to the flow of water while extending sufficiently longitudinally to rigidly support the housing.   
     
     
       2. The counter-rotating propeller system as claimed in claim 1 and further comprising: a thrust bearing operatively placed with respect to the outer propeller shaft to restrict its forward motion under load.   
     
     
       3. The counter-rotating propeller system as claimed in claim 1 and further including a bearing interposed between the inner and outer propeller shafts. 
     
     
       4. The counter-rotating propeller system as claimed in claim 3 wherein the bearing extends longitudinally for a distance generally commensurate with the distance along which the inner and outer propeller shafts extend. 
     
     
       5. The counter-rotating propeller system as claimed in claim 4 wherein the bearing is a cutlass bearing. 
     
     
       6. The counter-rotating propeller system as claimed in claim 5 and further including a second cutlass bearing operatively interposed between the drive shaft and the housing. 
     
     
       7. The counter-rotating propeller system as claimed in claim 6 and further comprising a bearing interposed between the outer propeller shaft and the housing. 
     
     
       8. The counter-rotating propeller system as claimed in claim 1 wherein the housing has a generally frusto-conical shape. 
     
     
       9. The counter-rotating propeller system as claimed in claim 8 wherein the aft end of the housing has a diameter that is sized commensurate with that of the propeller hubs. 
     
     
       10. The counter-rotating propeller system as claimed in claim 9 wherein the housing has a counter bore and said conversion means comprises a plurality of interconnected bevel gears that are mounted in the housing counter bore.